San Joaquin Valley Irrigation District Vulnerability to Groundwater Overdraft Based on Surface Water Allocation and Consumptive Water Use

Abstract:

California’s San Joaquin Valley is a global leader in food production but is highly vulnerable to hydroclimatic variability and water scarcity. Historically, local irrigation districts (IDs) have relied on groundwater to augment surface water supply, but overdraft and degradation have resulted in new regulatory limits on groundwater use through the Sustainable Groundwater Management Act (SGMA). Each ID is unique, with a complex combination of history, customer base, surface water portfolio, size, location, political capital, and socioeconomic status. As such, each ID is uniquely vulnerable to imposed groundwater scarcity and hydroclimatic shocks. This study spatially resolves how ID surface water allocations and consumptive water use contribute to groundwater overdraft vulnerability and its implication for sustaining agricultural production and local communities in an uncertain future. It also quantifies total applied water (TAW), consumptive water use (CWU) and groundwater overdraft per ID for the 2016 drought year by using crop classification data and a water footprint model to calculate CWU within ID boundaries and assumes that California appropriative water right’s allocation data are representative of TAW for each ID to deduce groundwater reliance. This study found that about 70% of the IDs analyzed in this study have been identified to rely on groundwater supply to counter surface water deficits to meet CWU of which ~31% contain disadvantaged communities within their service area boundaries. The total crop area within groundwater reliant ID totals ~9,066 km²; Kern and Tulare Counties contain more vulnerable IDs (n=12, n=13). Top crops grown in the 74-groundwater reliant IDs are almonds (n=17, 23%), grapes (n=9, 12%), and citrus (n=11, 15%). This study can assist decision-makers in IDs that are prone to not meeting SGMA sustainability targets by 2040 and to identify components of the food-water system capable of reducing overall vulnerability (i.e. changes in consumptive water use, alternative land uses, changes in crop composition) and building resilience to hydroclimatic shocks.